1. Field of the Invention
This invention relates to a method for the production of aziridines and N-vinyl amides. More particularly, this invention, in the production of aziridines and N-vinyl amides by the gas phase intramolecular dehydration respectively of an alkanolamine and an alkanolamide, relates to a method for producing the aziridines and the N-vinyl amides industrially advantageously by preventing a solid substance from forming and depositing in the decompressing system which is connected to the purifying step (vacuum distillation).
2. Description of the Related Art
Aziridines are cyclic amines that have an amino group of high reactivity. The aziridine compounds are widely known compounds in the industrial world as raw materials for medicines and agricultural chemicals and as raw materials for amine type polymers used as fiber processing agents and paper processing agents. Similarly, the N-vinyl amides are very useful compounds that are widely known in the industrial world as raw materials for medicines and agricultural chemicals.
It is well known that aziridines are produced by the gas phase intramolecular dehydration (hereinafter occasionally referred to as “dehydration reaction”) of alkanolamines. JP-A-04-217659, for example, discloses a method for the production of an aziridine, which comprises a step for forming an aziridine by the dehydration reaction of an alkanolamine, a step for collecting the produced aziridine by causing a reaction mixture containing the formed aziridine to contact the alkanolamine (collecting agent) used in the previous step, a step for purifying the aziridine by introducing the collected liquid containing the aziridine into a distillation column, and a step for recovering the alkanolamine in the collecting agent by introducing the bottom liquid occurring in the step of purification into the distillation column and distilling the bottom liquid in the presence of water. A similar technique is disclosed in U.S. Pat. No. 4,966,980.
By the dehydrating reaction of an alkanolamine, not only an aziridine is formed as the target product but also such amines as ammonia, methyl amine, and ethyl amine and such carbonyl compounds as acetaldehyde and acetone are formed as by-products. The by-produced carbonyl compounds may react with the aziridine, which is the target product, and form Schiff bases and ketimines. When the reaction mixture is subjected in its unaltered form to purification by distillation, therefore, the yield of the purification of an aziridine is unduly low. In the method of JP-A-04-217659, the reaction mixture containing the aziridines is brought into contact with the alkanolamine as the collecting agent so as to enable the carbonyl compound to react with the alkanolamine and undergo conversion into the Schiff bases and ketimines. Thereafter, the reaction mixture is distilled to separate amines and purify aziridines. The bottom liquid that occurs during the step of purification is distilled in the presence of water. The Schiff bases and the ketimines are decomposed into alkanolamines and carbonyl compounds and the alkanolamines are recovered.
Since the step of purification and the step of recovery are both carried out under reduced pressure, amines are extracted through the top of the distillation column at the step of purification and carbonyl compounds are extracted through the top of the distillation column at the step of recovery.
The present inventors have discovered that when the method disclosed in JP-A-04-217659 is carried out industrially, it can impose the following problems. When a single vacuum pump is used to decompress different distillation columns, amines and carbonyl compounds react inside vacuum lines and vacuum pumps that extend from the tops of the distillation columns. By this reaction, such solid substances as Schiff bases and ketimines are formed and these solid substances are suffered to clog the vacuum lines and the vacuum pumps. As a result, the control of pressure is rendered difficult and the operation of distillation is not allowed to proceed with stability. For the purpose of removing such clogging substances, it is necessary to stop the plant and wash the vacuum lines and the vacuum pumps. The efforts incur an economic burden and lower the productivity of the plant.
The problems mentioned above are not limited to the case of producing aziridines by the dehydrating reaction of alkanolamines but may occur similarly in the case of producing N-vinyl amides by the dehydrating reaction of alkanolamides. When alkanolamides are used as the raw materials, such amines as piperazine and alkyl piperazines, such aldehydes and ketones as propion aldehyde, methyl ethyl ketone, and N-butyl aldehyde are by-produced in addition to the N-vinyl amides as target products. When one and the same vacuum pump is used for the step of purification and the step of recovery, therefore, such solid substances as Schiff bases and ketimines are formed in the vacuum pumps and the vacuum lines similarly to the case of producing aziridines.
An object of this invention is to solve the problems mentioned above and provide a method for industrially advantageously producing aziridines by the dehydration reaction of an alkanolamine.
Another object of this invention is to provide a method for industrially advantageously producing N-vinyl amides by the dehydration reaction of an alkanolamide.